Method of forming folded-stack packaged device using progressive folding tool

ABSTRACT

An embodiment of the present invention includes a plunger, a heating element, and first and second arms. The plunger affixes a first unit to a second unit with adhesive. The first and second units are on a strip of a flexible tape. The strip is on a folding base unit. The folding base unit folds the first unit on top of the second unit. The heating element is attached to the plunger to cure the adhesive. The first and second arms are positioned on first and second sides of the plunger via first and second hinges, respectively, to secure the first and second units underneath the plunger. Another embodiment of the invention includes a first sub-assembly and a second sub-assembly. The first sub-assembly supports a first unit. The first sub-assembly, when activated, folds the first unit on top of a second unit. The first and second units are on a strip of a flexible tape. The second sub-assembly supports the second unit.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.10/261,335, filed Sep. 30, 2002 now U.S. Pat. No. 7,089,984. ThisDivisional Application claims the benefit of the U.S. patent applicationSer. No. 10/261,335.

BACKGROUND

1. Field

Embodiments of the invention relate to the field of packaging, and morespecifically, to folded-stack packaging.

2. Background

Chip scale technology offers many advantages in electronics packaging.One emerging packaging technique in chip scale technology is micro ballgrid array (μBGA) packaging. μBGA provides the smallest size, highestperformance, and best reliability of currently available packages.Folded-stack (fs) μBGA further improves board density and reliability.

Existing techniques for folded-stack packaged devices are typicallymanual, requiring boat-to-boat handling from singulation process to cureprocess. These techniques have a number of drawbacks. First, the processis slow and cumbersome. The packaged device units are processed througha number of discrete operations: saw singulation, first boat handling,folding and adhere, second boat handling, folding and curing, and thentraying. Second, it is expensive because several components (e.g., jigs)are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 is a diagram illustrating a micro ball grid array (μBGA)packaging layout according one embodiment of the invention.

FIG. 2 is a diagram illustrating a folded-stack μBGA packaged deviceaccording to one embodiment of the invention.

FIG. 3 is a diagram illustrating a tool assembly according to oneembodiment of the invention.

FIG. 4A is a diagram illustrating a first folding phase for the μBGApackaged device according to one embodiment of the invention.

FIG. 4B is a diagram illustrating continuation of the first foldingphase for the μBGA packaged device according to one embodiment of theinvention.

FIG. 4C is a diagram illustrating a second folding phase for the μBGApackaged device according to one embodiment of the invention.

FIG. 4D is a diagram illustrating continuation of the second foldingphase for the μBGA packaged device according to one embodiment of theinvention.

FIG. 5 is a flowchart illustrating a process to fold the μBGA packageddevice according to one embodiment of the invention.

FIG. 6 is a diagram illustrating a packaging assembly line forfolded-stack μBGA packaged devices according to one embodiment of theinvention.

FIG. 7A is a diagram illustrating a first unit trim station in thepackaging assembly line shown in FIG. 6 according to one embodiment ofthe invention.

FIG. 7B is a diagram illustrating an adhesive application station in thepackaging assembly line shown in FIG. 6 according to one embodiment ofthe invention.

FIG. 7C is a diagram illustrating a first folding and second unit trimstation in the packaging assembly line shown in FIG. 6 according to oneembodiment of the invention.

FIG. 7D is a diagram illustrating a second folding station in thepackaging assembly line shown in FIG. 6 according to one embodiment ofthe invention.

FIG. 7E is a diagram illustrating a tape de-dambar and pick and placestation in the packaging assembly line shown in FIG. 6 according to oneembodiment of the invention.

FIG. 8 is a diagram illustrating a top view of a packaging assembly linefor folded-stack μBGA packaged devices according to one embodiment ofthe invention.

FIG. 9 is a flowchart illustrating an assembly process for folded-stackμBGA packaged devices according to one embodiment of the invention.

DESCRIPTION

An embodiment of the present invention includes a plunger, a heatingelement, and first and second arms. The plunger affixes a first unit toa second unit with adhesive. The first and second units are on a stripof a flexible tape. The strip is on a folding base unit. The foldingbase unit folds the first unit on top of the second unit. The heatingelement is attached to the plunger to cure the adhesive. The first andsecond arms are positioned on first and second sides of the plungerrespectively, to secure the first and second units underneath theplunger. Another embodiment of the invention includes a firstsub-assembly and a second sub-assembly. The first sub-assembly supportsa first unit. The first sub-assembly, when activated, folds the firstunit on top of a second unit. The first and second units are on a stripof a flexible tape. The second sub-assembly supports the second unit.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures, and techniques have not been shown in order not toobscure the understanding of this description.

One embodiment of the invention may be described as a process which isusually depicted as a flowchart, a flow diagram, a structure diagram, ora block diagram. Although a flowchart may describe the operations as asequential process, many of the operations can be performed in parallelor concurrently. In addition, the order of the operations may bere-arranged. A process is terminated when its operations are completed.A process may correspond to a method, a program, a procedure, etc.

FIG. 1 is a diagram illustrating a micro ball grid array (μBGA)packaging layout 100 according to one embodiment of the invention. Thelayout 100 includes a tape carrier 120, and a flexible tape 130.

The tape carrier 120 is typically a metal frame to carry a number ofpackaged devices affixed on the flexible tape 130. The flexible tape 130is a rectangular tape that can be flexibly folded. The flexible tape 130may be a double-sided polyimide tape (e.g., Kapton or Upilex) having athickness of about 10 μm to 75 μm. The packaged devices are affixed onthe flexible tape 130 in a number of rows and columns. In oneembodiment, there are three rows and N columns. Typically values of Nare 16, 20, 24, 32, etc.

Each column corresponds to a strip of the flexible tape 130 and includesthree units: the first unit 140 ₁, the second unit 140 ₂, and the thirdunit 140 ₃. Each of the units includes a die affixed to a correspondingportion of the flexible tape 130. For example, the first unit 140 ₁, thesecond unit 140 ₂, and the third unit 140 ₃ include a first die, asecond die, and a third die, respectively, affixed to a first portion135 ₁, a second portion 135 ₂, and a third portion 135 ₃, respectively,of the strip. Each side of the flexible tape 130 may have a metal layerthat has leads and/or interconnections between the die. The die may beany semiconductor chip or devices such as memory device, flash memory,static random access memory (SRAM), dynamic random access memory (DRAM),logic devices, processing elements, etc. The die are affixed to theflexible tape 130 with die-attaching materials based on silicon orepoxy. The die may also be lead-bonded and encapsulated. The die areattached to the strip by solder balls.

The packaged devices on the flexible tape 130 are packaged and processedaccording to traditional packaging techniques. In one embodiment, thepackaging technique is the μBGA. The packaged devices on each strip orcolumn are folded in a stacking manner to form a folded-stack μBGA. Inthe following description, for illustrative purposes, the packageddevice will be referred to as a folded-stack μBGA. It is contemplatedthat the packaged device may use any suitable packaging techniques.

FIG. 2 is a diagram illustrating a folded-stack μBGA packaged device 200according to one embodiment of the invention.

The folded-stack device 200 includes first, second, and third die 210 ₁,210 ₂, and 210 ₃, respectively, and the flexible tape 130. As discussedabove, the first, second, and third die 210 ₁, 210 ₂, and 210 ₃ areattached to the flexible tape 130 via solder balls 210. The solder balls210 are micro grid array of soldering materials attached to the pads onthe flexible tape 130. The flexible tape 130 is folded in two folds. Inthe first fold, the first die 210 ₁ is positioned such that its surfaceis affixed to the surface of the second die 210 ₂ by an adhesive. Theaffixed first and second die 210 ₁ and 210 ₂ form a partially foldedunit. In the second fold, the third portion of the flexible tape 130attaching to the third die 210 ₃ is folded on top of the partiallyfolded unit. The surface of the third die 210 ₃ is affixed to the bottomside of the first portion of the flexible tape 130 by adhesive.

The folded-stack μBGA packaged device 200 as formed is compact andprovides high density and high reliability on a printed circuit board.The process to fold the μBGA packaged device 200 is performed in aprogressive manner in an assembly line that includes several stations.The folding process is efficiently performed by using a tool assemblyfor folding, affixing, and curing.

FIG. 3 is a diagram illustrating a tool assembly 300 according to oneembodiment of the invention. The tool assembly 300 includes a plungerassembly 310 and a folding base unit 360. The tool assembly 300 operateson a strip of the flexible tape 130 (shown in FIG. 1) which carries thefirst, second, and third units 140 ₁, 140 ₂, and 140 ₃, respectively.

The plunger assembly 310 includes a panel 315, a plunger 320, a heatingelement 330, and two arms 342 and 344. The panel 315 is a rectangular orsquare plate of suitable material such as metal. The panel 315 has ahole located in the middle to allow the plunger to travel up and down.The plunger 320 is a rod of sufficient length and is made of suitablematerial such as metal. The rod may be of any suitable shape such ascylinder. In the initial, or home position, the plunger 320 is retractedupward. The position shown in FIG. 3 is when the plunger 320 is abouthalf way down, or half way up. The plunger 320 may move upward anddownward through the hole of the panel 315 under action of an activationunit (not shown). When forced to move downward, the plunger 320 affixesthe first unit 140 ₁ to the second unit 140 ₂ with adhesive. The firstunit 140 ₁ is folded to be on top of the second unit 140 ₂ by thefolding base unit 360.

The heating element 330 is attached to the plunger 320 at a distal end.The heating element 330 may also be integral to the plunger 320. Theheating element 330 is made of thermally conducting material such asmetal or alloy. Heat may be generated by applying an electrical voltageacross wires internal to the heating element 330. The heating element330 thermally cures the adhesive between the first and second units 140₁ and 140 ₂.

The first and second arms 342 and 344 are positioned on the first andsecond sides of the plunger 320 around the panel 315 via first andsecond hinges 322 and 324, respectively. They are used to align thefirst unit 140 ₁ when folded op top of the second unit 140 ₂ and whenthe third unit 140 ₃ is folded on top of the folded first unit 140 ₁.The first and second arms 342 and 344 move around the first and secondhinges 322 and 324. The position shown in FIG. 3 is an open position. Inthe initial, or home position, the first and second arms 342 and 344 arein a closed position when they are approximately vertical and directlyfacing to each other. A cam mechanism is used to mechanically connectthe vertical movement of the plunger 320 and the swinging movement ofthe first and second arms 342 and 344. When the plunger 320 extendsdownward, the first and second arms 342 and 344 swing open. When theplunger 320 retracts upward, they swing closed. When they move inwardtoward each other, they secure the first and second units 140 ₁ and 140₂ underneath the plunger 320. This is typically done when the plunger320 moves downward to press on the folded first unit 140 ₁ and thesecond unit 140 ₂. The first and second arms 342 and 344 extend outwardaround the first and second hinges 322 and 324, respectively, to releasethe first and second units 140 ₁ and 140 ₂ so that they can betransferred or moved to the next area. This can be done when the plunger320 moves upward after affixing and curing the first and second units140 ₁ and 140 ₂. The first and second arms 342 and 344 may extend undersome spring action that is activated when the plunger 320 moves upward.

The first and second arms 342 and 344 may also have first and secondstoppers 352 and 354, respectively, facing inward toward the plunger320. The first and second stoppers 352 and 354 act as a guide slot tosecure units in place to be folded and affixed. For illustrativepurposes, the second stopper 354 is shown to be above the first stopper352, just enough to hold down the folded units on the sides of theflexible tape and not touching the mold unit. The exact location of thestoppers 352 and 354 on the first and second arms 342 and 344,respectively, depends on the thickness of the unit to be folded andaffixed.

The folding base unit 360 provides support for the flexible tape 130 andthe first, second, and third units 140 ₁, 140 ₂, and 140 ₃. The plungerassembly 310 is typically positioned to be directly above the middlerow, or the second unit 140 ₂. The folding base unit 360 also folds thefirst unit 140 ₁ on top of the second unit 140 ₂ to form a partiallyfolded unit in a first folding phase. In a second folding phase, thefolding base unit 360 folds the third unit 140 ₃ on top of the partiallyfolded unit. Note that when used in two separate phases, there may betwo separate tool assemblies 200, one for the first folding phase andone for the second folding phase. The tool assemblies 200 for the twophases are almost identical. The differences may include the dimensions,the location of the stoppers 352 and 354, the travel length of theplunger 320 (which may be adjusted), and the orientation of the foldingbase unit 360, etc. Conceptually, therefore, the folding base unit 360may be considered as a unit to fold a “first unit” on top of a “secondunit”. In the first folding phase, the “first unit” is the first unit140 ₁ and the “second unit” is the second unit 140 ₂. In the secondfolding phase, the “first unit” is the third unit 140 ₃ and the “secondunit” is the partially folded unit including the first unit 140 ₁affixed to the second unit 140 ₂.

The folding base unit 360 includes first, second, and thirdsub-assemblies 370, 380, and 390 to support the first, second, and thirdunits 140 ₁, 140 ₂, and 140 ₃, respectively. These sub-assemblies may beinterconnected together by some interconnection mechanism.Alternatively, they may be integrated together in a single unit.

The first sub-assembly 370, when activated, folds the first unit on topof the second unit. As noted above, when the folding base unit 360 isused in the first folding phase, the first unit to be folded is thefirst unit 140 ₁ and the second unit is the second unit 140 ₂. When thefolding base unit 360 is used in the second folding phase, it folds thethird unit 140 ₃ on top of the partially folded unit. It should also benoted that in the first folding phase, the correspondence between thesub-assemblies and the units on the flexible tape 130 is reverse fromthat in the second folding phase. In the first folding phase, the first,second, and third sub-assemblies 370, 380, and 390 support the first,second, and third units 140 ₁, 140 ₂, and 140 ₃. In the second foldingphase, the first and second sub-assemblies 370 and 380 support the thirdunit 140 ₃ and the partially folded unit (formed by the first unit 140 ₁affixed to the second unit 140 ₂). Normally, in the second foldingphase, the third sub-assembly 390 is not required.

The first sub-assembly 370 includes a block 372 and a rocking mechanism375. The block 372 is an angles block having a slanted surface toprovide a resting position for the first unit 140 ₁ in the first foldingphase (or the third unit 140 ₃ in the second folding phase). In thefollowing discussion, for clarity, references will be made to the firstunit and the second unit without reference numerals. It should beunderstood that when used in the first folding phase, the term “firstunit” refers to the first unit 140 ₁ and the term “second unit” refersto the second unit 140 ₂. When used in the second folding phase, theterm “first unit” refers to the third unit 140 ₃ and the term “secondunit” refers to the partially folded unit. The inclination or slope ofthe slanted surface depends on the dimensions of the first unit 140 ₁and the mechanical characteristics of the rocking mechanism 375. Ingeneral the slope of the slanted surface is such that the folding actionperformed by the rocking mechanism 375 is facilitated. The steeper theslope, the less force the rocking mechanism 375 is exerted on the firstunit. The block 372 has a hollow or vacuum space beneath the slantedsurface to provide housing for the rocking mechanism 375. The rockingmechanism 375 includes a rocking lever 365 and a cam 367. The rockinglever 365, when activated, causes the cam 367 to move or rotate to pushthe first unit from the resting position to fold the first unit on topof the second unit.

FIG. 4A is a diagram illustrating a first folding phase 400 for the μBGApackaged device according to one embodiment of the invention. The firstfolding phase 400 includes a first act 410, a second act 420, a thirdact 430, a fourth act 440, and a fifth act 450.

In the first act 410, the strip of the flexible tape 130 with the threeunits 140 ₁, 140 ₂, and 140 ₃ is on the folding base unit 360. Inaddition, the first unit 140 ₁ has been punched out. The plungerassembly 310 is positioned directly above the second sub-assembly 380. Afirst adhesive 425 and a second adhesive 427 are dispensed on thesurface of the second unit 140 ₂ and the surface of the third unit 140₃, respectively.

In the second act 420, the rocking lever 365 is activated to rotate thecam 367. The cam 367 pushes the first unit 140 ₁ out of the restingposition to be folded on top of the second unit 140 ₂. The first andsecond arms 342 and 344 help keeping the first unit 140 ₁ being bent orfolded aligned with the second unit 140 ₂. The plunger assembly 310 thenmoves down.

In the third act 430, the plunger assembly 310 secures the partiallyfolded unit with its two arms. The surface of the first unit 140 ₁ is incontact with the surface of the second unit 140 ₂. The first adhesive425 acts to glue the two units together to form a partially folded unit435. The plunger 320 of the plunger assembly 310 is then activated tomove downward to apply sufficient force on the first unit 140 ₁ to affixthe first unit 140 ₁ to the second unit 140 ₂. The heating element 330then generates heat to thermally cure the adhesive 425.

FIG. 4B is a diagram illustrating continuation of the first foldingphase for the μBGA packaged device according to one embodiment of theinvention. The continuation includes a fourth act 440 and a fifth act450. In the fourth act 440, the plunger assembly 310 is moved upwardwhile the plunger 320 is still down. In the fifth act 450, the plunger320 is retracted upward to the home position. This concludes the firstfolding phase.

FIG. 4C is a diagram illustrating a second folding phase 455 for theμBGA packaged device according to one embodiment of the invention. Thesecond folding phase 455 includes a first act 460, a second act 470, athird act 480, a fourth act 490, and a fifth act 495. Note that in thesecond folding phase, the strip with the third unit 140 ₃ and thepartially folded unit 435 has been transferred from the first foldingphase to the folding base unit such that the third unit 140 ₃ rests onthe slanted surface of the first sub-assembly 370 and the partiallyfolded unit 435 is on the second sub-assembly 380. The third unit 140 ₃has been punched out.

In the first act 460, the plunger assembly 310 is positioned directlyabove the second sub-assembly 380. The second adhesive remains on thesurface of the third unit 140 ₃. In the second act 470, the rockinglever 365 is activated to cause the cam 367 to rotate to push the thirdunit 140 ₃ toward the partially folded unit 435 such that the third unit140 ₃ is folded on the bottom of the second portion of the strip to forma fully folded unit 475. The plunger assembly 310 moves toward thepartially folded unit 435. In the third act 480, the plunger assembly310 secures the fully folded unit by the two arms. The plunger 320 thenmoves downward to exert sufficient force on the third unit 140 ₃ toaffix the third unit 140 ₃ to the partially folded unit via the secondadhesive 427. The heating element 330 then generates heat to thermallycure the second adhesive 427 and the entire folded unit. After the thirdact 480, the plunger assembly 310 moves upward and the two arms extendto release the fully folded unit.

FIG. 4D is a diagram illustrating continuation of the second foldingphase for the μBGA packaged device according to one embodiment of theinvention. The continuation includes the fourth act 490 and the fifthact 495. In the fourth act 490, the plunger assembly 310 is moved upwardwhile the plunger 320 is still down. In the fifth act 495, the plunger320 is retracted upward to the home position. This concludes the secondfolding phase.

FIG. 5 is a flowchart illustrating a process 500 to fold the μBGApackaged device according to one embodiment of the invention. Note thatthe process 500 is applicable for both the first folding phase and thesecond folding phase. Again, the terms “first unit” and “second unit”are interpreted accordingly as discussed above.

Upon START, the process 500 places the strip of the three units on thefolding base unit secured by vacuum underneath the second unit withcavity clearance for the solder balls (Block 510). Next, the process 500positions the plunger assembly directly above the second unit of thestrip and moves the plunger assembly downward just above the second unit(Block 520). Then, the process 500 extends the rocker lever to push-foldthe first unit, seated on the slanted or angled block, into the plungerassembly (Block 530). The first unit is to be folded on top of thesecond unit.

Then, the process 500 keeps the first unit being folded and aligned withthe second unit by the two arms (Block 550). Next, the process 500affixes the first unit to the second unit with the adhesive by extendingthe plunger down (Block 560). The plunger continues the folding motionon the first unit until the first unit is secured on top of the secondunit.

Then, the process 500 cures adhesive and the first and second units bythe heating element attached to the tip of the plunger (Block 570).Next, the process 500 moves the plunger assembly upward to release thecured unit (Block 580). The folded first and second units are now readyto be transferred or moved to other area. Then, the process 500 movesthe plunger upward to the home position (Block 590). The process 500 isthen terminated.

FIG. 6 is a diagram illustrating a packaging assembly line 600 forfolded-stack μBGA packaged devices according to one embodiment of theinvention. The assembly line 600 includes a first unit trim station 620,an adhesive application station 630, a prefold, cure, and second trimstation 640, a final fold and cure station 650, and a flex tapesingulation and pick and place station 660, a transport assembly 670,and a lifting assembly 680.

The transport assembly 670 rolls the tape carrier 120 through thestations for processing. The tape carrier 120 carries a number of stripsof flexible tape as described in FIG. 1. The process is progressive orpipeline such that when one strip is processed by one station, anotherstrip is processed at another station at the same time. The assemblyline starts at the ON LOAD area where the packaged devices on theflexible tape are loaded into the tape carrier 120. As the tape carrier120 progresses through the stations, the packaged devices are processedand eventually become a folded-stack μBGA devices to be transferred ordelivered to a tray at the OFF LOAD area. The process is efficient asthe tape carrier 120 fully enters the stations, all the stations arebusy processing each phase of the process.

The transport assembly 670 includes a rotator 672, a guide rod 674, aguide rail 675, a transport arm 676, and a transport finger 678. Therotator 672 rotates to advance the guide rod 674 with screw type in alinear motion along the guide rail 675 to move the tape carrier 120through the processing stations. The lifting assembly 680 moves the tapecarrier 120 up and down to allow punching the strip out to be placed onthe folding base unit 360. The lifting assembly 680 has two rows oflifters/cylinders 682 and 684 placed along the stations and two rows ofguide pins 686 and 688. The number of lifters/cylinders and guide pinsalong each row depends on the space and processing requirements of themanufacturing plant. When the lifters/cylinders 682 and 684 are inextended, or up position, the tape carrier 120 is transported to thenext station one unit pitch at a time via the transport finger 678. Whenthe lifters/cylinders 682 and 684 are in the home, or down position, thetape carrier 120 is not transported. During this time, the pre-cut,adhesive dispense, folding, and unit singulation are done simultaneouslyat all the processing stations.

The packaged devices on the tape carrier may be arranged as 3×N where Nis the number of columns or strips. The number of rows may not belimited to three. Depending on the folding configuration, the toolassembly shown in FIG. 3 may be modified to accommodate differentarrangements.

The exact spacing of the stations depends on the particular set-up ofthe assembly line. Regardless of the spacing or distance between thestations, each strip on the tape carrier 120 goes through all 6stations. Typically, the processing times of the stations areapproximately equal so that the tape carrier 120 can be moved at regularor uniform speed. However, as is known by persons of ordinary skill, thetransport assembly 670 can be controlled to have non-uniform speed.

FIG. 7A is a diagram illustrating a first unit trim station 620 in thepackaging assembly line shown in FIG. 6 according to one embodiment ofthe invention.

In the first unit trim station 620, the first unit of a column or stripis trimmed, cut, or punched out. The first unit corresponds to the firstrow. When the first unit is trimmed and punched out, it is bent downwardwith respect to the horizontal direction. The strip is then moved to theadhesive application station 630.

FIG. 7B is a diagram illustrating an adhesive application station 630 inthe packaging assembly line shown in FIG. 6 according to one embodimentof the invention.

In the adhesive application station 630, the adhesives are dispensed onthe surface of the second unit 140 ₂ and the third unit 140 ₃. The firstunit 140 ₁ is bent downward. The adhesive can be dispensed by anadhesive dispenser located above the units. Then, the tape carrier 120moves the strip to the first folding and second unit trim station 640.

FIG. 7C is a diagram illustrating a first folding and second unit trimstation 640 in the packaging assembly line shown in FIG. 6 according toone embodiment of the invention. Note that the term “pre-fold” and“final fold” folding phase may be replaced by “first folding phase” or“second folding phase”.

In the first folding and second unit trim station 640, the strip isprocessed by the tool assembly as shown in FIG. 4A. The first unit 140 ₁is folded on top of the second unit 140 ₂. The plunger unit affixes thefirst unit 140 ₁ to the second unit 1402 with the adhesive dispensed onthe surface of the second unit 140 ₂. The plunger unit then cures theadhesive. The affixed first and second units 140 ₁ and 140 ₂ form thepartially folded unit 435. At the same time, the third unit 140 ₃ istrimmed, cut, and punched out. The strip is then moved to the secondfolding station 650.

FIG. 7D is a diagram illustrating a second folding station 650 in thepackaging assembly line shown in FIG. 6 according to one embodiment ofthe invention.

In the second folding station 650, the strip is processed by the toolassembly as shown in FIG. 4B. The third unit 140 ₃ is then folded on topof the partially folded unit. The plunger assembly then affixes thethird unit 140 ₃ to the partially folded unit 435 with the adhesivedispensed on the surface of the third unit 140 ₃. The plunger assemblythen cures the adhesive. The affixed third unit 140 ₃ and the partiallyfolded unit form a fully folded unit 710. Then, the strip with the fullyfolded unit 710 is moved to the flex tape singulation and pick and placestation 660.

FIG. 7E is a diagram illustrating a flex tape singulation and pick andplace station 660 in the packaging assembly line shown in FIG. 6according to one embodiment of the invention.

The flex tape singulation and pick and place station 660 removes ordetaches the flexible tape from the fully folded unit to form afolded-stack packaged device. The pick and place station then picks thefolded-stack package device and transfers to the tray at the OFF LOADarea.

FIG. 8 is a diagram illustrating a top view of a packaging assembly linefor folded-stack μBGA packaged devices according to one embodiment ofthe invention.

As seen from the top, at any time, the six stations process six stripsor columns 810, 820, 830, 840, 850, and 860 on the flexible tape on thetape carrier. The strip 810 is processed by the first unit trim station620 as shown in FIG. 7A. The strip 820 is processed by the adhesiveapplication station 630 as shown in FIG. 7B. The strip 830 is processedby the first folding and second unit trim station 640 as shown in FIG.7C. The strip 840 is processed by the second folding station 650 asshown in FIG. 7D. The strip 850 is processed by the flex tapesingulation and pick and place station 660 as shown in FIG. 7E. At theend of the assembly line, the final folded-stack packaged device locatedin the second row is removed and transferred to the OFF LOAD area.

FIG. 9 is a flowchart illustrating an assembly process 900 forfolded-stack μBGA packaged devices according to one embodiment of theinvention.

Upon START, the process 900 cuts and punches the first unit from thestrip of the flexible tape (Block 910). Next, the process 900 appliesadhesive to the second and third units (Block 920). Then, the process900 folds the first unit on top of the second unit, affixes the firstunit to the second unit with adhesive, and thermally cures the adhesiveand the first and second units (Block 930). The affixed first and secondunits form a partially folded unit.

Next, the process 900 cuts and punches the third unit from the strip(Block 940). Then, the process 900 folds the third unit on top of thepartially folded unit, affixes the third unit to the partially foldedunit with adhesive, and thermally cures the third unit and the partiallyfolded unit. The cured third unit and partially folded unit form a fullyfolded unit (Block 950). Next, the process 900 detaches the fully foldedunit from the flexible tape using singulation punch, activates the pickand place mechanism to deliver the folded stack packaged device in trayin the off-load area (Block 960). The process 900 is then terminated.

While the invention has been described in terms of several embodiments,those of ordinary skill in the art will recognize that the invention isnot limited to the embodiments described, but can be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

1. A method comprising: folding a first unit on top of a second unit bya folding base unit, the first and second units being on a strip of aflexible tape, the strip being on the folding base unit; affixing thefirst unit to the second unit with adhesive by a plunger; curing theadhesive by a heating element attached to the plunger; securing thefirst and second units underneath the plunger by first and second armspositioned on first and second sides of the plunger, respectively; andextending the first and second arms outward to release the first andsecond units.
 2. The method of claim 1 wherein folding the first unit ontop of the second unit comprises folding a first micro ball grid array(μBGA) packaged device on top of a second μBGA packaged device.
 3. Themethod of claim 1 further comprising affixing a first die of the firstunit on a first portion the strip.
 4. The method of claim 3 furthercomprising: affixing a second die of the second unit on a second portionof the strip; and dispensing the adhesive on a surface of the seconddie.
 5. The method of claim 3 further comprising dispensing the adhesiveon a surface of the first unit.
 6. The method of claim 5 furthercomprising affixing a second die to a third die of the second unit, thesecond unit being affixed on second and third portions, respectively, ofthe strip.
 7. The method of claim 1 wherein extending the first andsecond arms comprises: moving the plunger upward.
 8. The method of claim1 wherein the flexible tape is a double-sided polyimide tape.
 9. Themethod of claim 1 wherein the flexible tape has a thickness from 10 μmto 75 μm.
 10. The method of claim 1 wherein the first unit includes afirst die.
 11. The method of claim 10 wherein the second unit includes asecond die.
 12. The method of claim 10 wherein the second unit includesa partially folded unit having a second die and a third die affixed toeach other.